Most of waste plastics hitherto have been dumped by reclaiming lands with the same or incinerating the same, and have never been used as useful resources. This waste disposal by way of reclaiming the lands has difficulties in the ensuring of the sites to be reclaimed, and in stable hardening of such sites. On the other hand, the disposal by way of incinerating the waste plastics has disadvantages, such as the damage to the incinerators, generation of organic gases and offensive odors, and emission of CO2.
To solve these problems, the Containers and Packaging Recycling Law was instituted in 1995 in Japan, so as to obligate the recovering and recycling of plastics. This trend of recovering and recycling products containing plastics is prevailing in association with the enforcement of a variety of recycling laws.
Recently, under such circumstances, there is a trial such waste plastics are to be recycled and reused as material resources. For example, the following patent literatures 1-5 suggest methods for decomposing the plastics by using of supercritical or subcritical water, as a reaction media, in order to provide decomposed products to be collected.
Since these methods, however, randomly decompose the plastics, it is difficult to provide a certain quality of decomposed product.
In order to solve such problems, for example, the following patent literature 6 suggests a method for decomposing, with subcritical water, a thermosetting resin of a polyester composed of a polyalcohol and a polybasic acid, which has been crosslinked by a crosslinking agent, under the thermal decomposition temperature of the thermosetting resin, in order to provide monomers to be recycled as materials for newly producing a thermosetting resin as well as copolymers between the crosslinking agent and the polybasic acid, such as styrene-fumaric acid copolymers.    Patent Literature 1: JP-T-56-501205    Patent Literature 2: JP-A-57-4225    Patent Literature 3: JP-A-5-31000    Patent Literature 4: JP-A-6-279762    Patent Literature 5: JP-A-10-67991    Patent Literature 6: WO 2005/092962